Bountiful rains? Yeah, the forecast models nailed it

Forecast models often struggle with getting precipitation right on the upper Texas coast. There are lots of reasons why, but the essence of the problem is this: A lot of ingredients have to come together at just the right time for really heavy rain to fall. Now many of these ingredients, such as a very moist atmosphere, are in place a lot of the time, so there can be some false positives when it comes to predicting rainfall.

So we were all a little concerned that the bountiful rains forecast for last night might not occur. But I’m happy to report that the forecast models called it correctly as Houston set a rainfall record for Tuesday and received more rain in a single day than it has in more than two years.

Let’s look at how accurately the WRF model (a mesoscale model created to try and model localized weather effects) predicted for rain totals during today’s event:

That model was run on its supercomputer on Monday at 7 a.m., or nearly a full day before the heavy rain fell. What struck me about the forecast at the time was the clear delineation between very wet areas (i.e. central Harris County) and areas to the east, such as Beaumont, which were forecast to get just a few tenths of an inch.

I was concerned this “dry line” might fall further to the west leaving most of Houston mostly dry, and noted so on Facebook. Fortunately it did not. In fact, the model nailed the location of this dry line almost perfectly. Here’s a look at preliminary rainfall estimates from the last 24 hours:

Actual rainfall amounts during the last 24 hours. (NOAA)

In any case it was very nice to see the rainfall Houston got, especially in a way that minimized disruptions to the normal course of business and without too much flooding. Our drought situation suddenly looks much better heading into summer.

Have you considered joining the Community Collaborative Rain, Hail and Snow networks (CoCoRAHs)? They need people who are willing to report rainfall (and snowfall and hail) amounts so that meteorologists can get more ground truth to improve their forecasts. They’ve got a great website at:http://www.cocorahs.org/

They didn’t nail it. Everyone came real close though. Maybe in ten years they will nail it. They need to start launching weather balloons in Houston and shrink the grid some. It’s too spread out. The closest other one is out of State. Too far away. The grid is too spread out.